Automotive trailers customarily are equipped with sliders which support the rear wheels of, and which can be shifted limited distances forwardly and rearwardly relative to, those trailers. Each such trailer has longitudinally-extending structural members with spaced openings therein, and the slider has locking pins that can be selectively moved into those openings to lock the trailer and slider together for conjoint movement or can be withdrawn from those openings to permit limited relative movement between that trailer and that slider. A large manually-operated lever is mounted on the slider; and it can be operated by the truck driver or by a helper to selectively withdraw the locking pins from the openings therefor and to subsequently force the locking pins into those openings.
If a helper is available, he can use the large manually-operated lever to withdraw the locking pins from the openings in the longitudinally-extending structural members of the trailer. Thereafter, the driver can actuate a switch in the cab of the tractor to lock the slider-supported wheels against movement, and then use the motive power of the tractor to move the trailer forwardly or rearwardly relative to the slider. The helper can indicate to the driver when the desired openings in the longitudinally-extending structural members of the trailer have been moved into register with the locking pins; and then the driver can brake the tractor to hold those pins and openings in register while the helper uses the manually-operated lever to force the pins into the adjacent openings in the longitudinally-extending structural members. It is desirable for the driver to have a helper available to him when the trailer is to be shifted relative to the slider, because a very considerable force usually is required to operate the lever to pull the pins out of the openings in the longitudinally-extending structural members of the trailer. Also, a helper is useful in determining when the appropriate openings are in register with the locking pins. If a driver does not have a helper, he may find it extremely difficult, and even impossible, to apply sufficient force to the lever to withdraw the pins from the openings in the longitudinally-extending structural members of the trailer. Thereafter, he would have to alight from the cab, check the position of the desired openings in the longitudinally-extending structural members of the trailer relative to the locking pins on the slider, and re-enter the cab to "inch" the trailer relative to the slider, and then repeat the procedure until the desired openings are in exact registry with the locking pins.
It is never easy to use the manually-operated lever to unlock and re-lock a slider relative to a trailer--even when the driver has a helper. It is much more difficult to use the manually-operated lever to effect the unlocking and re-locking of the trailer and slider when the driver does not have a helper. When the driver--with or without a helper--must provide relative movement between the trailer and the slider in icy or rainy weather, the task of using the manually-operated lever to effect an unlocking and re-locking of the trailer and slider becomes unpleasant as well as very difficult.